1. Field of the Invention
The present invention relates to a disposable syringe mainly used in medical treatment.
2. Description of the Prior Art
A syringe needle of the syringe after use is attached with patient's blood and the like containing pathogenic bacteria etc. When the syringe needle attached with blood or the like is reused, there is a possibility of triggering a secondary infection. To prevent such a secondary infection, a number of disposable syringes are used. As the disposable syringe, for example, like the syringe as disclosed in Japanese Patent Laid-Open No. 31681/1995 (hereinafter referred to as "a conventional syringe"), a syringe (a lead-in type syringe needle) of the system is generally known where the syringe needle attached with blood or the like after use is inserted into a syringe body of the syringe and discarded after kept in a state of being untouchable from outside.
The conventional syringe comprises; a syringe body; a piston sliderably inserted from one end of the syringe body; a smaller-diameter portion formed at the other end in the opposite direction of one end of the syringe body; a needle support detachably supported by the smaller-diameter portion; a syringe needle supported by the needle support; a stopper formed in a tip of the smaller-diameter portion for preventing the needle support from slipping off in the other end direction of the syringe body; an locking projection from a tip of the axis center direction of the piston; and a locking hole disposed on a syringe side of the needle support for engaging with said locking projection when the piston is pressed in, and wherein, after the locking projection is inserted into and engaged with the locking hole by pressing in the piston, the syringe needle with the needle support is pulled into the syringe and stored there by pulling out the piston.
the conventional syringe is widely used even today in medical field and the like. However, the inventor was not satisfied with it and continued to engage in research work by seeking for a method of improving usable facility. What the inventor aimed at is whether removal of the needle support from the syringe body could be made more smoother than before. To make removal of the needle support smooth, a locking structure with the needle support and the syringe body may be made into a structure easy to disengage. This is because, if the structure is easy to disengage, a tensile force at the time when the needle support is pulled into the syringe body together the syringe needle may be to be weak.
However, if the structure easy to disengage is adapted, a trouble tends to arise where a sealability between the needle support and the syringe body is lost and parenteral solution leaks out from the syringe body. This is particularly true of a syringe of the system where the syringe needle is used with the needle support is attached. That is, since a compressive force at the time when the syringe needle is attached acts upon this locking structure, the locking structure can not be extremely weak no matter how smooth drawing out should be made. To satisfy at once a conflicting demand for both making drawing out (removal) smooth and sufficiently keeping sealability in high level is the object to be solved of the present invention.